The present invention relates generally to an optical system for correcting thermally-induced wavefront distortion in a crystal, and more particularly to a variable applied stress device used with a crystal to correct for optical distortion in the crystal caused by thermal factors.
An optical system in which a crystal is utilized to generate a laser beam for experimentation and measurement should transmit a beam that is free of optical distortions. The crystal is usually a long rod used to generate a moderate power laser beam or may comprise an electro-optical or nonlinear optical element to modify the beam. The optical effects generated in a crystal due to heating from a high power or moderate power laser beam occur even though the beam is expected to provide good beam quality and high polarization purity after passing through the crystal. However, optical distortion and birefringence result from a perfectly linearly polarized moderate power laser beam through a heated crystal rod. The correction of the optical wavefront distortion and birefringence is sought if thermally induced. Distortion and birefringence depend on the temperature variation within the crystal generated by the absorption of the laser beam. The heating of the crystal produces thermal-stress-strain effects. The thermal-stress-strain effects distort the output beam from the crystal.
Systems and methods to correct wavefront distortion and birefringence currently employ multiple actuator deformable mirrors, which are very expensive and cumbersome. Numerous actuator signals must be produced and transmitted to each actuator and the interactions between the various actuators and their various signals must be overcome. A system and method is therefore desired which will decrease the number of signals and complexity associated with employing multiple actuator deformable mirrors.
The above and other objects are provided by an optical correction system and method in accordance with the preferred embodiments of the present invention. In one preferred embodiment, the optical correction system includes a stress application device that applies a stress to a crystal to minimize optical distortions created in a transmitted beam. The stress application device is coupled to a computational device that determines the optical distortion of the transmitted beam. A beam sensor and wavefront reconstructor is coupled to the computational device and provides a measurement of the transmitted beam. The beam sensor and wavefront reconstructor receives a refracted beam from a beamsplitter that divides the transmitted beam into a reflected beam and the refracted beam. The reflected beam, which originally includes a degree of optical distortion, is corrected via the application of a precise degree of stress to the crystal.
The system and method of the present invention thus forms an effective xe2x80x9cclosed-loopxe2x80x9d system by which the optical distortion resulting from thermal factors experienced by the crystal can be continuously monitored, in real time, and precisely corrected.
The optical correction system and method of the present invention also does not add significantly to the overall cost of the optical system. It further does not add to the complexity of the optical system, does not require the production and transmission of signals, and can be used with a variety of crystal geometries.